1. Field
Embodiments described herein relate generally to a camera calibration apparatus which is an on-vehicle camera apparatus having a plurality of on-vehicle cameras for taking images outside a vehicle so as to display them for a driver and performing camera calibration at camera installation time, etc.
2. Background
There is conventionally known an on-vehicle camera apparatus having the following configuration. In this on-vehicle camera apparatus, a plurality of cameras are mounted on a vehicle, and the cameras are used to acquire images of areas (front side, back side, left side, and right side) surrounding the vehicle. Then, images (overhead images) in which the viewpoints thereof are converted to those above the vehicle are created and then synthesized. The resultant image is further synthesized with the image (illustration, etc.) of the vehicle to obtain a top-view image. Displaying the overhead image facilitates grasping of a state of the vehicle and its surrounding environment, which, for example, supports driver's driving at the time when the vehicle is parked in a parking space. The overhead view is an image viewed from a virtual viewpoint set at, e.g., a position above the vehicle. By changing the position of the virtual viewpoint, appearance of the overhead view can be made different.
In conventional on-vehicle camera apparatus, the installation position, installation angle, and installation height of the camera are set to values that have previously been designed. However, an error occurs in the actual installation time, so that some misalignment may occur in the connection portions between a plurality of images photographed by a plurality of cameras at the time of image synthesis, with the result that the connecting portions in a synthetic image become discontinuous. In order to cope with this problem, there is proposed a calibration apparatus that sets a calibration pattern within a photographing area and calibrates the coordinates of a photographed image based on the photographed calibration pattern.
For example, a square-shaped calibration pattern having a side of about 1 m to 1.5 m is set in photographing area of each of four cameras, and the calibration patterns are used to position the images photographed by the respective cameras before image synthesis. In this method, it is necessary to set special calibration patterns for calibration on the ground surface, etc., and another calibration pattern for specifying the position of the vehicle at an accurate position.
Further, in the case of a calibration apparatus that detects the four corners (feature points) connecting white lines representing a parking space of a parking lot and uses the four feature points to calculate camera parameters (camera installation position, camera installation angle, focal distance, etc.), the number of feature points to be detected becomes large, so that it is necessary to perform the detection from a position to some extent away from the white lines and, in the case where the feature points are detected using front, back, left, and right cameras, the movement amount is increased due to a change of the vehicle's direction. Further, it is necessary to manually adjust the position of the vehicle or set feature points on the vehicle.